Breather vent... old to new?

Discussion in 'Airheads' started by headtube, Jan 3, 2019.

  1. headtube

    headtube Been here awhile

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    Still working on the 'new to me' R75/5. I've been debating whether or not to replace the original breather vent to the new reed-valve type. The bike has never run in my possession (yet) and it is in bits and pieces presently. Should I keep the original in place till it runs, or get the updated model vent. There are probably plenty of /5's running around with original breather vents that operate just fine.

    What do you guys think? Any advantages? If it ain't broke, don't fix it?
    #1
  2. SuperTENERE

    SuperTENERE Adventurer

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    "If it ain't broke, don't fix it........."
    #2
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  3. infinityedge

    infinityedge Been here awhile

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    I went with the "eh, I've got it apart this much and am already ordering crap from motobins, might as well" approach.

    Probably a waste of time and money, but isn't that the crux of airheadom?
    #3
  4. Disston

    Disston ShadeTreeExpert

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    I think the originals are rare. Seems the updating of this part is one of the most common modifications known in Airheadom. Seems the most common reason given is the Turkey Valve can break which is not a good thing. Don't know if there is any actual other good reason. Maybe there is but I don't think it's ever mentioned.

    Oh yeah. Another reason for this mod is often to eliminate the Turkey Gobble sound of the Turkey Valve. That sound never bothered me. I thought it was distinct. But I also don't have it anymore. I think I changed mine many years ago because it was broken but I may have done it because of all the hype. Don't remember.

    If one still does have the fiber disk Turkey Valve and the disk gets broken it can be repaired by making one, a fiber disk, from a piece of circuit board or something. Details were in Oak's "Ask Oak" column many years ago. The part is not sold by BMW.
    #4
  5. Renner

    Renner combustophile Supporter

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    Do it as a performance upgrade. :deal
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  6. Pokie

    Pokie Just plain Pokie.

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    Turkey valve became a reality with the additional crank case pressure of the R90s. An R75 shouldn't need to new valve, unless you just want something to do.
    #6
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  7. 190e

    190e Long timer

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    You can get the turkey gobble on the smallest of airheads if there is excessive crankcase pressure but if you have overhauled the engine and fitted new seals that shouldn't happen so you shouldn't get the turkey gobble noise. I still have the original disc which I modified many years ago by drilling a 1mm hole through it. I believe it's not a damaged disc that makes the noise but too good a seal. The small hole relives the perfect seal of the disc.

    Where the reed valve is said to really work better is sustained high revs so your decision may depend on how the bike is to be ridden.
    #7
  8. Plaka

    Plaka Brevis illi vita est

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    If it Ain't broke, don't fix it. Easy thing to get in to any time. You have real work to do on that bike. No time to be dickin' around. Get. It. Running. Don't look for make work.

    I have the old disk type out of my /5 and a spare reed type out of my RT and a reed type in the RS. I'm stocked forever, and don't anticipate needing to replace any of them.
    #8
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  9. headtube

    headtube Been here awhile

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    OK. I'll keep it in place till she's running. Now that I know it sounds like a turkey I look forward to hearing that gooble sound as I ride along. :roflThe 1mm hole seems like a plan if I need a tad more venting. I'll try that first if' n there's an issue. If that doesn't work I'll reach for the new reed-valve breather when the time comes. :thumb
    #9
  10. nobbylon

    nobbylon Been here awhile

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    Gives the oldies a bit more character :)
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  11. tsADV

    tsADV Been here awhile

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    I vote for the " . . don't fix it" (yet) alternative. Get it running first.

    FWIW, my 75/5 sometimes had the turkey gobble noise when idling. So I took the breather valve apart, checked that it was working as intended, and that the valve disc sat at the correct notch on the shaft (one for 75s, another for 60 and 50s). And drilled the 1 mm hole. Still gobbling. Eventually I found out that the gobbling noise was due to a leaking main rear oil seal (more and more oil accumulating on the shelf). I could pull out the leaky seal with two fingers. New seal in, no more leaks, no more gobble noise :-)
    #11
  12. Plaka

    Plaka Brevis illi vita est

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    Pressure in the crankcase lifts the disk and crank case blow by goes around the lifted disk into the carbs. If you drill a hole in the disk you defeat this. The disk leaks and lifts less against its' spring. Not a good idea. The disk also fails to seal when the crankcase is sucking, that is, when both pistons are moving outwards. It's supposed to be a one way vale, not a one way valve that kinda leaks backwards. Any backward leaaking will draw mix from the carbs into the crank case. As in gas and air.

    Make sense?

    The disc valve is made of many pieces held together with a clip. Expensive. The reed type is two pieces held together with a rivit (IIRC). Whole lot cheaper. That is what was behind the change. I have both if you want a pic, I just gotta dig them out. (hassle)
    #12
  13. Disston

    Disston ShadeTreeExpert

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    The gobble sound made by the turkey valve is only present at idle, usually.

    The leaky rear seal making the gobble sound that sounds very much like the turkey valve is usually hard to diagnose.
    #13
  14. Plaka

    Plaka Brevis illi vita est

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    mechanics stethoscope.
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  15. bmwrench

    bmwrench Long timer

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    Close. The reed and limiter strap are retained by a very small screw, so 4 pieces. Whatever the case, it works far better than the disc. I was, and am, bemused that Oak went to the effort of duplicating it.

    I've occasionally wondered if BMW developed the reed valve after looking at the Geitl/Schuster Superbike, which used a reed valve from a chainsaw.
    #15
  16. Plaka

    Plaka Brevis illi vita est

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    I've noticed that gurus often have rather different opinions on things. My guess would be that the disk valve is "softer" and opens more. But after considerable effort, I can find neither of mine.
    #16
  17. 2ThumpinPumpkins

    2ThumpinPumpkins Been here awhile

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    upload_2019-1-4_22-41-36.png
    #17
  18. 190e

    190e Long timer

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    Yes I understand how it works to pump down the crankcase pressure and I can't disagree with the logic but the area of the 1mm hole is not a big deal at less than 1% of the total area and the thing is it stopped the gobble which has never returned. If it hadn't worked I would have change it for a reed valve. The idea for the hole came from Mike Fishwick.
    #18
  19. Plaka

    Plaka Brevis illi vita est

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    You scared the little guy! It was afraid you would savage it further and shut up.


    So who is Mike Fishwick? Am I supposed to bow at the alter of Mike Fishwick?Got to keep me up to speed here. But I got over playing that BS with OAK a LONG tie ago.
    #19
  20. robtg

    robtg Long timer

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    Plaka, the pharmacy called, your meds. are ready.
    #20
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